The present invention is related generally to the field of losses introduced in an optical light guide resulting from the need to abruptly change the directional orientation of the path of the optical light guide and, more particularly, to a highly advantageous miniature bend arrangement and associated method employing a particular configuration of fiber optic light guide members which avoids the introduction of significant bend losses.
Attention is immediately directed to FIG. 1 which is a representation of FIG. 6 of U.S. Pat. No. 5,138,676 issued to Stowe et al and hereinafter referred to as the '676 patent. Optical fibers used, for example, in communications systems are known to produce losses with respect to light signals traveling on the fibers with the introduction of a sufficiently sharp bend. At the same time, it is often desirable to introduce such sharp bends for purposes such as, for instance, device miniaturization. In this regard, a typical optical fiber may be bent at a diameter of approximately 50 mm before introducing appreciable bend losses. One approach in attempting to resolve this problem is described in the '676 patent, as illustrated by FIG. 1. The latter shows a structure, generally indicated by the reference numeral 5, configured for introducing a sharp bend in a light path. Structure 5 includes a jacket 10 surrounding an optical fiber 32 which is, in turn, mounted in a right angle grooved supporting structure 34. The fiber enters the structure at reference number 36 and exits at 38 with its core 39 shown. Fiber 32 includes a reduced diameter section 18 which is bent at approximately a 90.degree. angle. The diameter of the reduced diameter section is approximately 15 microns as compared to a normal diameter of approximately 125 microns. A polished end face 40 is included at one end which may be positioned adjacent to another device or fiber. A cladding 42 surrounds core 39 of the fiber. It is noted that a 180 degree bend using this reduced diameter section technique is disclosed in an article by David W. Stowe and Frederick J. Gillham entitled "Miniature Fiber Bends Offer Flexibility in Component and Circuit Design."
Having generally described structure 5 of FIG. 1, it should be appreciated that one underlying feature of the structure resides in substantially reducing the diameter of section 18 of fiber 32 in a way which removes the cladding. Initially, this fiber is surrounded by jacket 10 and is configured with cladding 42. To remove the cladding, the jacket is removed, as illustrated, and reduced diameter section 18 is produced, for example, in an etching process in combination with drawing. The cladding is removed at least to an extent that the interface between the reduced diameter section and the surrounding air is relied on to produce internal reflection of light traveling around the bend and through the reduced diameter section. Upon such removal of the cladding, the numerical aperture of the fiber itself in this region is submitted to be so low as to not serve as a useful light guide without further provisions. That is, the numerical aperture in the reduced diameter region is now determined based upon the difference between the index of refraction of the fiber as a whole and the index of refraction of the surrounding medium, in this instance, air. Typically, this numerical aperture is quite high, resulting in low bend losses for light traveling through reduced diameter section 18. While structure 5 generally serves its intended purpose, several disadvantages have been discovered, as will be described immediately hereinafter.
Still referring to FIG. 1, it is important to note that reduced diameter section 18 must be exposed to air (or some other suitable medium) along its entire length. Hence, the requirement for supporting structure 34. That is, reduced diameter section 18 must not contact anything but air to avoid adversely affecting the index of refraction produced through the cooperation of the air and the reduced diameter section. This requirement is submitted to be disadvantageous in and by itself. Moreover, the significance of achieving a sharp bend in the fiber is considered to be overshadowed by the disadvantageous requirement of supporting structure 34. The latter limits the usefulness of structure 5 particularly with regard to producing miniaturized devices, since such a housing must accompany the bent fiber. In future device generations this limitation is considered as being unacceptable. Moreover, it is submitted that structure 5 is complex and, as such, factory production environments are mandated using precision fixtures resulting in a relatively expensive final product.
The present invention provides a highly advantageous and heretofore unseen mini-bend arrangement and associated method which eliminates the foregoing disadvantages and which provides still further advantages.